Chemistry: Ionic Bonding

What is an Ion?

• An ion is an atom or molecule that has gained or lost one or more electrons.

Sodium and Chlorine Reaction

• Sodium (Na): Wants to lose an electron to have a full outer shell.
• Chlorine (Cl): Wants to gain an electron to have a full outer shell.
• Chemical Reaction:
  • Sodium gives an electron to chlorine.
  • Sodium becomes a positive ion (cation).
  • Chlorine becomes a negative ion (anion).
  • Result: Formation of Na⁺ and Cl⁻ ions, creating sodium chloride (NaCl).

Ionic Compounds

• Have giant structures with millions of positive and negative ions.
• Form regular structures known as lattices (e.g., cubic for NaCl).

Cations and Anions

• Cations: Positive ions formed by metal atoms losing electrons.
• Anions: Negative ions formed by non-metal atoms gaining electrons.

Determining Ionic Charges

• Group Number Influence:
  • Group 1 elements (e.g., Na) form +1 ions.
  • Group 2 elements (e.g., Be) form +2 ions.
  • Group 3 elements (e.g., Al) form +3 ions.
• Transition Metals: Can have different charges (e.g., Fe²⁺, Fe³⁺).

Dot and Cross Diagrams

• Represent electron transfers in ion formation.
• Metal ions lose all electrons in the outer shell, shown by no dots or crosses.
• Non-metal ions gain electrons, shown by additional dots or crosses.

Negative Ion Charge Calculation

• Formula: 8 minus the group number (e.g., Chlorine in Group 7 becomes Cl⁻).

Polyatomic Ions

• Important Ions to Know:
  • CO₃²⁻ (Carbonate)
  • SO₄²⁻ (Sulfate)
  • NO₃⁻ (Nitrate)
  • OH⁻ (Hydroxide)

Factors Affecting Ionic Bond Strength

• Charge of Ions: Higher charges result in stronger electrostatic attractions.
• Ion Size: Smaller ions result in stronger attractions due to reduced distance between charges.

Example Cases

• Strongest Bond: Higher charges (+2/-2) and smaller ion size.
• Weakest Bond: Lower charges (+1/-1) and larger ion size.

Practice Questions

• Draw dot and cross diagrams for the first 10 elements and their ions.
• Explain the factors affecting the strength of ionic bonds.